derived ba physical and electrical characterization of sol...

Physical and electrical characterization of sol-gel derived BaxSr1-xTiO3 thin films of various composition

ratios and thicknesses

By

Nurhafizah binti Ramli

(0830110279)

A thesis submitted in fulfillment of the requirements for the degree of Master of Science (Microelectronic Engineering)

School of Microelectronic Engineering UNIVERSITI MALAYSIA PERLIS

2011

© This item is protected by original copyright

i

UNIVERSITI MALAYSIA PERLIS

DECLARATION OF THESIS Authors’ full name : Nurhafizah binti Ramli

Date of Birth : 27 November 1984

Title : Physical and electrical characterization of sol-gel derived BaxSr1-

xTiO3 thin films of various composition ratios and thicknesses.

Academic Session : 2008 – 2011

I hereby declare that the thesis becomes the property of Universiti Malaysia Perlis (UniMAP) and to

be placed at the library of UniMAP. This thesis is classified as:

CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*

RESTRICTED (Contains restricted information as specified by the organization where research was done)*

OPEN ACCESS I agree that my thesis is to be made immediately available as hard copy or on-line open access (full text)

I, the author, give permission to the UniMAP to reproduce the thesis in whole or in part for the

purpose of research or academic exchange only (except during a period of ___ years, if so requested

above).

Certified by:

__________________ __________________

SIGNATURE SIGNATURE OF SUPERVISOR

__________________ ___________________

(NEW IC NO. /PASSPORT NO.) NAME OF SUPERVISOR

Date: ______________ Date: ____________


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ACKNOWLEDGEMENT

How should I begin this note of appreciation? There have been so many people

involved that I will feel guilty if I don’t mention them here. Therefore, if any of them reads

this and finds that they are not listed here, I would like to say thank you for your help.

First of all, I am deeply grateful to my supervisor, Mejar Assoc. Prof. Zaliman Sauli

for the continuous support, effort and was very willing to take me under his wing. I also

feel so honored to have Leftenan R. Charan as my co-supervisor for his patience,

motivation, enthusiasm and immense knowledge in helping me complete my thesis. He

played such an important role in helping me complete my work. I would also like to take

this opportunity to thank Assoc. Prof. Dr Johari Adnan, my second co-supervisor as well as

Dean of School of Microelectronic Engineering for his encouragement to fulfill my task.

In my daily work I have been blessed with a friendly and cheerful group of

researchers. So, in this brief and short note I would like to expand my appreciation to those

people who spend their time and shared their knowledge; Gium, Steven, Mydin, Bojjie,

Emma, Syud and many others for their endless support. Without you guys, I would be in

disarray.

I am also grateful to the failure analysis and cleanroom staff; En. Bahari, En.

Hafizz, En. Hafiz, En. Zul, En. Din for keeping the lab in such superb condition.

Last but not least, to my family, my parents and sisters for their love, patience and

support throughout my studies.


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TABLE OF CONTENTS

PAGE

DECLARATION OF THESIS

ACKNOWLEDGEMENTS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF ABBREVIATIONS

ABSTRAK

ABSTRACT

i

ii

iii

vi

vii

ix

x

Xi

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Overview of Barium Strontium Titanate 1

1.3 Problem Statement 3

1.4 Research Objectives 4

1.5 Research Scope 5

1.6 Dissertation Layout 5

CHAPTER 2 A REVIEW ON BST

2.1 Introduction 7

2.2 An Overview of Ferroelectricity 7

2.3 Properties of Barium Strontium Titanate 10


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2.4 Overview and Previous Work of BST thin films 12

2.5 Summary 30

CHAPTER 3 RESEARCH METHODOLOGY

3.1 Introduction 33

3.2 Solution Preparation of BaxSr1-xTiO3 34

3.3 BaxSr1-xTiO3 Solution Deposition Process 37

3.3.1 Cleaning Process 38

3.3.2 Dry Oxidation Process 39

3.3.3 Platinum Deposition 40

3.3.4 BaxSr1-xTiO3 Deposition Process 40

3.3.5 Heat Treatment Process 41

3.4 Physical Characterization of BaxSr1-xTiO3 Thin Films 42

3.4.1 BaxSr1-xTiO3 Thin Films Verification with XRD Analysis 43

3.4.2 BaxSr1-xTiO3 Thin Films Surface Characterization with Atomic Force

Microscopy

43

3.4.3 Thickness Measurement of BaxSr1-xTiO3 Thin Films 44

3.5 Electrical Characterization of BaxSr1-xTiO3 Thin Films 45

3.5.1 Fabrication Process of the Capacitor 45

3.5.2 Electrical Characterization of BaxSr1-xTiO3 thin films 47

3.6 Summary 48

CHAPTER 4 RESULTS AND DISCUSSION

4.1 Introduction 49

4.2 X-Ray Diffraction (XRD) Analysis 49

4.3 Physical Characterization 54

4.4 Electrical characterization 65


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4.5 Summary 82

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Introduction 84

5.2 Conclusion 84

5.3 Future Work Recommendation 86

REFERENCES 87

APPENDIX A 92

APPENDIX B 95

LIST OF PUBLICATIONS 99


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LIST OF TABLES

TABLE

PAGE

2.1 Preparation techniques of BST thin films 13

3.1 The amount of material used in preparing BaxSr1-xTiO3

solution

37

4.1 Lattice parameters of BaxSr1-xTiO3 films at room temperature 53

4.2 Surface morphology of BaxSr1-xTiO3 thin films 54

4.3 3-D Image of BaxSr1-xTiO3 Thin Films Surface of 4 Layer

Thickness

56

4.4 Grain size of BaxSr1-xTiO3 thin films 58

4.5 Average rms surface roughness BaxSr1-xTiO3 thin films for

each layer

60

4.6 Thickness of BaxSr1-xTiO3 thin films for each layer 63

4.7 Film thickness, grain size, dielectric constant, loss tangent and

dielectric tunability of Ba0.5Sr0.5TiO3 thin films

67

4.8 Film thickness, grain size, dielectric constant, dielectric loss

and dielectric tunability of Ba0.6Sr0.4TiO3 thin films

73



75



77

4.11 Dielectric constant of BaxSr1-xTiO3 thin films with different

thickness

78


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LIST OF FIGURES

FIGURE

PAGE

2.1 Transition characteristic of ferroelectric material 9

2.2 The ABO3 perovskite structure of BaxSr1-xTiO3 (Adikary,

2003)

10

2.3 Curie temperature of BaxSr1-xTiO3 as a function of

stoichiometry (Remmel et al., 1999)

11

2.4 Lattice parameter of BaxSr1-xTiO3 versus composition at

room temperature

12

3.1 Summary of the overall physical and electrical

characterization process of the BaxSr1-xTiO3 film

34

3.2 Process flow of BaxSr1-xTiO3 solution preparation 36

3.3 Complete BaxSr1-xTiO3 deposition process 38

3.4 Heat treatment process of BaxSr1-xTiO3 solution 42

3.5 Scanning location on the sample with AFM 44

3.6 BST thin film capacitor 45

3.7 Overall process of fabricated BST capacitor 46

3.8 SPA probe position 47

4.1 XRD pattern of Ba0.5Sr0.5TiO3 thin films 50




4.5 Grain size of BaxSr1-xTiO3 thin films as a function of layers 59

4.6 Average rms surface roughness of BaxSr1-xTiO3 thin films

as a function layers

61

4.7 Step profile of 2 layer Ba0.8Sr0.2TiO3 thin films 62

4.8 Step profile of 4 layer Ba0.7Sr0.3TiO3 thin films 62

4.9 Thickness of BaxSr1-xTiO3 thin films as a function layers 64


viii

4.10 r-V characteristics of Ba0.5Sr0.5TiO3 thin films with 4

different thickness

66

4.11 Film thickness dependence of the dielectric constant and

tunability of Ba0.5Sr0.5TiO3 thin films

68

4.12 Film thickness dependence of the dielectric constant and

tunability of BaxSr1-xTiO3 thin films

69

4.13 Grain size dependence of the dielectric constant and

tunability of Ba0.5Sr0.5TiO3 thin films

70

4.14 Grain size dependence of the dielectric constant and

tunability of BaxSr1-xTiO3 thin films

71


different thickness

72


different thickness

74


different thickness

76

4.18 The variation dielectric constant of BaxSr1-xTiO3 thin films

as a function of film thickness

80

4.19 The variation dielectric tunability of BaxSr1-xTiO3 thin films

as a function of film thickness

81

4.20 The variation dielectric loss of BaxSr1-xTiO3 thin films as a

function of film thickness

82


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LIST OF ABBREVIATIONS

BST = Barium strontium titanate

AFM = Atomic Force Microscopy

XRD = X-ray Diffraction

PVD = Physical Vapor Deposition

RTA = Rapid Thermal Annealing

Ba = Barium

Sr = Strontium

Pt = Platinum

Si = Silicon

SiO2 = Silicon dioxide

Al = Aluminum

Rms = Root means square

DRAM = Dynamic Random Access Memory

TC = Curie temperature

RF = Radio Frequency

MOCVD = Metal Organic Chemical Vapor Deposition


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Pencirian fizikal dan elektrikal berasaskan teknik sol-gel untuk menghasilkan filem

nipis BaxSr1-xTiO3 untuk pelbagai nisbah komposisi dan ketebalan

ABSTRAK

Antara pelbagai bahan-bahan dielektrik, barium strontium titanate telah dikaji secara meluas kerana mempunyai pemalar dielektrik yang tinggi, kehilangan dielektrik yang rendah dan tunabiliti yang tinggi. Barium strontium titanate adalah komposisi yang bergantung kepada suhu Curie yang menurun secara linear dengan peningkatan jumlah Sr dalam komposisi tersebut. Dalam kajian ini, filem nipis barium strontium titanate dengan empat komposisi berbeza; Ba0.5Sr0.5TiO3, Ba0.6Sr0.4TiO3, Ba0.7Sr0.3TiO3 dan Ba0.8Sr0.2TiO3 telah disediakan dengan menggunakan teknik sol-gel dan difabrikasi atas substrat Pt/SiO2/Si. Filem nipis itu dikristalkan dengan baik, padat, rata dan bebas retak yang diperolehi dengan suhu penyepuhlindapan pada 800 C. Pemalar dielektrik, tunabiliti, dan kehilangan dielektrik menunjukkan hubungan erat dengan mikrostruktur filem. Pemalar dielektrik, tunabiliti dan kehilangan dielektrik bertambah dengan bertambahnya saiz butiran dan ketebalan filem. Variasi pemalar dielektrik dengan fungsi voltan untuk filem nipis Ba0.5Sr0.5TiO3 dan Ba0.6Sr0.4TiO3 tanpa pengutuban spontan, menunjukkan kewujudan sifat paraelektrik dalam suhu bilik. Bagaimanapun, filem nipis Ba0.7Sr0.3TiO3 dan Ba0.8Sr0.2TiO3 mempunyai bentuk lengkung kupu-kupu menunjukkan kewujudan sifat ferroelektrik. Pemalar dielektrik tertinggi dan tunabiliti, 485.02 dan 34.75 % diperhatikan dalam komposisi Ba0.7Sr0.3TiO3 pada ketebalan 447.6 nm kerana suhu Curie Ba0.7Sr0.3TiO3 hampir kepada suhu bilik. Kerja ini menunjukkan pencirian berjaya dalam sifat-sifat fizikal dan elektrik berbilang lapisan filem nipis BaxSr1-xTiO3 dengan nisbah Ba dan Sr yang berbeza.


xi

Physical and electrical characterization of sol-gel derived BaxSr1-xTiO3 thin films of

various composition ratios and thicknesses

ABSTRACT

Among the various dielectric materials, barium strontium titanate has been

extensively studied due to its high dielectric constant, low dielectric loss and high tunability. Barium strontium titanate is a composition dependent to Curie temperature, which decreases linearly with the increasing of Sr amount in the composition. In this study, barium strontium titanate thin films with four different compositions; Ba0.5Sr0.5TiO3, Ba0.6Sr0.4TiO3, Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 and four different thicknesses were prepared by using sol-gel technique and deposited on Pt/SiO2/Si substrates. The well-crystallized, dense, smooth and crack-free thin films are obtained through annealing process at temperature of 800 C. The dielectric constant, tunability and dielectric loss shows strong relationship with the films microstructure. The dielectric constant, tunability and dielectric loss increases as the grain size and film thickness increases. The variations of dielectric constant as a function of voltage for Ba0.5Sr0.5TiO3 and Ba0.6Sr0.4TiO3 thin films are devoid of any spontaneous polarization, which indicates that the thin film is paraelectric in room temperature. However, Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 thin films with butterfly-shaped curves show the existence of ferroelectric nature. The highest dielectric constant and tunability, 485.02 and 34.75 % were observed in Ba0.7Sr0.3TiO3 composition at thickness of 447.6 nm due to the Curie temperature of Ba0.7Sr0.3TiO3 is close to room temperature. This work demonstrates successful physical and electrical characterization of multiple layers of BaxSr1-xTiO3 thin films to its different composition ratios of Ba and Sr.


1

CHAPTER 1

INTRODUCTION

1.1 Introduction

This chapter explains the overview of the research done followed by the problem

statement. The objectives and scope of this research are described in detail. Finally the

dissertation of layout of this thesis is briefly explained.

1.2 Overview of Barium Strontium Titanate

Barium strontium titanate (BaxSr1-xTiO3/ BST) material is one of the

ferroelectric materials which attract great interest among researchers to study its

electrical properties due to high dielectric constant and composition dependent to Curie

temperature (Roy & Krupanidhi, 1993). Barium strontium titanate compounds are the

continuous solid solution of barium titanate (BaTiO3) and strontium titanate (SrTiO3).

The introduction of Sr atoms to the A site of BaTiO3 lattice substitute the Ba atoms will

change the Curie temperature of BaxSr1-xTiO3. The Curie temperature of BaxSr1-xTiO3

system decreases linearly with the increase of Sr amount in the BaTiO3 lattice which

enables the paraelectric-ferroelectric transition temperature to be tailored by adjusting

the barium-to-strontium ratio for specific application.


2

There are few techniques available to fabricate the BST such as radio frequency

(RF) magnetron sputtering (Oh et al., 2007), metal organic chemical vapor deposition

(MOCVD) (Bogert, 1999), pulsed laser deposition (Zhu et al., 2006), soft-solution

processing (Shi, Yao & Zhang, 2005) and sol-gel process (Wang, Uusimäki &

Leppävuori, 1997). Among these techniques, sol-gel technique which involves the

usage of liquid solution mixture as a starting material offers a homogenous distribution

of elements at molecular level, high purity, ease of composition control and better

homogeneity. The lower cost of the equipment makes it a great method for preparing

new solutions with different compositions. Sol-gel technique also offers easier

deposition on large and complex area substrate for thin films fabrication.

Ferroelectric barium strontium titanate thin films have been widely investigated

due to its potential in microelectronic devices such as thin films capacitors (Kawakubo

et al., 1998), dynamic random access memory (DRAM) (Horikawa et al., 1993),

(Kumar & Manavalan, 2005), (Cho et al., 1997), infrared sensors (Zhu et al. 2004),

microwave devices (Wang et al. 2003), and hydrogen gas sensor (Zhu et al., 2000). This

is mainly because of its high dielectric constant, low dielectric loss, large electric-field

tunability, long lifetime and good temperature stability.

The previous work of other researchers show that the electrical properties;

dielectric constant, dielectric loss, leakage current and dielectric tunability of barium

strontium titanate thin films is affected by the composition of the films that changed the

Curie temperature. The film thickness, grain size, surface roughness, deposition

technique and type of dopant also influence the electrical properties of barium strontium

titanate thin films (Zhu et al., 2006), (Hu, Yang & Zhang, 2008), (Guiying, Ping, &

Dingquan, 2007). Therefore, the electrical behavior of BST is extremely dependent on


3

its material properties, including its stoichiometry, microstructure and thickness of

the films.

1.3 Problem Statement

Ferroelectric materials are being widely pushed to the forefront for usages in

microelectronic field. In this aspect, taking into consideration of the ferroelectric

materials capability of high dielectric constant function, it has good potential as a

capacitive device. Barium strontium titanate is vastly being researched in the area of

ferroelectric and piezoelectric areas, so this material is chosen in this work to study its

characteristic in both physical and electrical properties. Many theories and findings have

been brought forward in regards of correlation between physical and electrical

properties. These relationships are pivotal in device fabrication and functional parameter

tuning. To the best of the author’s knowledge, most of the previous work done focused

on single layer and multiple ratios of BaxSr1-xTiO3 composition for the thin films

physical and electrical property characterization. Work on multiple thickness or layers is

virtually not existence. In this work, multiple layer deposition and its correlation to

multiple ratios of BaxSr1-xTiO3, physical and electrical were investigated.


4

1.4 Research Objectives

The main objective of this work is to study the physical and electrical properties

of BST thin films by using sol-gel technique. The sub-objectives of this research are:

1. To prepare BaxSr1-xTiO3 solutions using sol-gel technique by varying barium-to-

strontium ratio with x=0.5, 0.6, 0.7, 0.8.

2. To deposit BaxSr1-xTiO3 solutions on Pt/SiO2/Si substrate with multiple layers

noted as 1 layer, 2 layer, 3 layer and 4 layer for physical characterization

including microstructure and thickness of the films.

3. To deposit Al/BaxSr1-xTiO3/Pt layer to produce capacitor in order to study the

electrical characteristics of the BaxSr1-xTiO3 films.

4. To determine correlation between the microstructure of BaxSr1-xTiO3 thin films

with the electrical properties.


5

1.5 Research Scope

In this work, the BaxSr1-xTiO3 thin films are prepared by using sol-gel technique.

The BaxSr1-xTiO3 solutions are deposited on Pt/SiO2/Si substrates by spin coating

process in order to study the microstructure of the films. The microstructure of the films

consists of the surface roughness and the grain size. The dots of Aluminum are

deposited on BaxSr1-xTiO3/Pt/SiO2/Si to produce metal/ferroelectric/metal layer to study

the electrical properties of the BaxSr1-xTiO3 thin films. The barium-to-strontium ratio is

varied with x=0.5, 0.6, 0.7 and 0.8 in order to study the effect of microstructure and

electrical properties of the thin films with four different thicknesses noted as 1 layer, 2

layer, 3 layer and 4 layer.

1.6 Dissertation Layout

This dissertation is divided into five chapters as Introduction, Overview of

Barium Strontium Titanate, Research Methodology, Results and Discussions and finally

the Conclusion.

The first chapter describe a brief review of the material used, problem statement,

objectives and scope of this research.

Chapter two covers review on BST and previous work on related topic by other

researchers.


6

Chapter three discusses the flow and process of the work done. The preparation

of the BaxSr1-xTiO3 solution is explained in this chapter and also the characterization of

the thin films.

Chapter four presents the results obtained from physical and electrical

characterization works. The first part displays the XRD pattern of the BST thin films.

Physical characterization consists of surface analysis and grain size is discussed. The

study of electrical characterization of BaxSr1-xTiO3 thin films in sandwiched of

Al/BST/Pt is also discussed in this chapter.

Finally, in chapter five, conclusion of overall results has been done with some future

work recommendation.


7

CHAPTER 2

A REVIEW ON BST

2.1 Introduction

This chapter is divided to three subsections which are the overview of

ferroelectricity, properties of barium strontium titanate and previous work done by other

researchers on barium strontium titanate thin films. The barium strontium titanate films

have been studied with different parameters which are preparation technique of the

barium strontium titanate films, film composition, film thickness, crystalline

temperature, etc which influences the electrical properties of the film itself.

2.2 An Overview of Ferroelectricity

Ferroelectricity is an electrical phenomenon of ferroelectric materials that

exhibit a spontaneous polarization in which the direction of the polarization can be

switched by the application of an external electric field. This phenomenon was

discovered by J. Valasek in 1920 during his study on the analogy between the magnetic

properties of ferromagnetic and the dielectric properties of Rochelle Salt (Gonzalo &

Jiménez, 2005). Barium titanate, BaTiO3, the first perovskite ferroelectric was

discovered during the early 1940’s in the United States, Russia and Japan. In 1945 and


8

1946, Von Hippel, and Wul and Goldman demonstrated first ferroelectric switching in

BaTiO3. Thus followed switching found in other perovskites, which is in KNbO3 and

KtaO3 discovered by Matthias in 1949, in LiNbO3 and LiTaO3 by Matthias and

Remeika in 1949 and in PbTiO3 by Shirane, Hishima and Suzuki in 1950 (Gonzalo &

Jiménez, 2005).

Ferroelectric materials with higher dielectric constant has a low dielectric loss

and high dielectric tunability compared to ordinary insulating substance. This makes

ferroelectric materials a good candidate for a variety of applications such as high

dielectric capacitors, tunable microwave devices, DRAM (dynamic random access

memory) capacitor, pyroelectric sensors, piezoelectric transducers, and electro optic

devices. This wide range of applications is mainly attributed to the phase transitions in

ferroelectrics. Most of the ferroelectric materials transforms to paraelectric cubic phase

above a transition temperature called Curie temperature, TC. The ferroelectric materials

change from paraelectric cubic phase to ferroelectric tetragonal phase below the TC. The

phase transition of ferroelectrics due to temperature is shown in Figure 2.1 (Manavalan,

2005).


9

Figure 2.1: Transition characteristic of ferroelectric material

In ferroelectric phase, the dielectric permittivity also known as the dielectric constant

(r), increases as the temperature increase while in the paraelectric phase, the dielectric

constant decreases with increase in temperature according to the Curie-Weiss,

휀 = 휀 + ≈ (2.1)

where C is the Curie constant, TC is the Curie temperature and T is temperature. The

dielectric constant reaches its maximum value at TC and for T TC, r severely

decreases. In ferroelectric phase, a highly non-linear loop or hysteresis loop is observed

that reveals that the material has memory (Haertling, 1999)). In the paraelectric phase,

without spontaneous polarization, the dielectric constant is still high and suitable for


10

tunable microwave and DRAM applications. One of the promising ferroelectric

materials is strontium-doped barium titanate (BaxSr1-xTiO3) compound due to high

dielectric constant and composition dependent Curie temperature (Roy & Krupanidhi,

1993).

2.3 Properties of Barium Strontium Titanate

Barium strontium titanate (BaxSr1-xTiO3) compounds are continuous solid

solution of barium titanate (BaTiO3) and strontium titanate (SrTiO3). The introduction

of Sr atoms to the BaTiO3 lattice substitutes the Ba atoms which will influence the

crystalline structure and its properties (Adikary, 2003). BaTiO3 and SrTiO3 adopt ABO3

perovskite structure because of its crystal structure is in the group of material with the

mineral name calcium titanate (CaTiO3). Figure 2.2 shows the ABO3 perovskite

structure of BaxSr1-xTiO3. A (Ba or Sr) represents the large cations located at the corners

of the unit cell, B (Ti) represents the smaller cations located at the body center and O is

the oxygen atoms positioned at the face centers.

Figure 2.2: The ABO3 perovskite structure of BaxSr1-xTiO3 (Adikary, 2003)

Ba or Sr


11

The substitution of Ba2+ ion with Sr2+ ion to the A site of the BaTiO3 crystal

structure is found to reduce the Curie temperature of BaTiO3 while maintaining its high

dielectric constant. The structure, dielectric and ferroelectric properties of BaxSr1-xTiO3

generally depends on the Sr content because the Curie temperature of BaxSr1-xTiO3

system decreases linearly towards room temperature with the increasing amount of Sr in

the BaTiO3 lattice as shown in Figure 2.3. The decreasing amounts of TC enable the

paraelectric-ferroelectric transition temperature to be tailored by adjusting the barium-

to-strontium ratio for specific application.

Figure 2.3: Curie temperature of BaxSr1-xTiO3 as a function of stoichiometry

(Remmel et al., 1999)

BaTiO3 has a paraelectric cubic phase above its Curie temperature at about 120

C while at room temperature, BaTiO3 exhibit tetragonal perovskite structure. The

tetragonality of BaxSr1-xTiO3 system decreases with the increasing of Sr content thus at

room temperature, the BaxSr1-xTiO3 with higher Ba content is tetragonal while with

higher Sr content is cubic. Therefore, the BaxSr1-xTiO3 with higher Ba content is

ferroelectric and tetragonal at room temperature.

The ferroelectric properties of BaxSr1-xTiO3 generally depend on the

tetragonality of the structure because smaller tetragonal value of c/a ratio may not be


12

sufficient to create separation and spontaneous polarization. Figure 2.4 shows the lattice

parameter (a and c) of BaxSr1-xTiO3 as a function of Sr (mol %) content at room

temperature. From Adikary, it is reported that BaxSr1-xTiO3 shows a complete solid

solubility over all compositions with a cubic structure at room temperature for 0 ≤ x ≤

0.3, becoming tetragonal for 0.3 ≤ x ≤ 1 which shown in Figure 2.4 which x is refer to

the Ba content.

Figure 2.4: Lattice parameter of BaxSr1-xTiO3 versus composition at room temperature

2.4 Overview and Previous Work of BST thin films

BST thin films received a large interest because of its potential in the application

of microelectronic devices due to high dielectric constant, relatively low dielectric loss

tangent and large dielectric field tunability (Chen et al., 2006). In general, a thin film is

a layer of material ranging from several nanometers to several micrometers in thickness

and is grown on a substrate. The relationship between the film and substrate influences

the characteristics of BST thin films (Su & Button, 2001, Su et al., 2003, Yi et al., 2002

& Koutsaroff et al., 2002). Some of the common materials used as a substrate are


derived ba physical and electrical characterization of sol...

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